Primarily, it's because they're more spherical. They're shinier and much much bigger and prettier too. They excrete a polymer that acts as a phenomenal lubricant and is often used on spacecraft to prevent overheating of the equipment due to friction. Furthermore, my genital excretions can be used as a powerful sunblock to prevent skin damage caused by UV rays, not to mention they're a potent aphrodisiac. Finally, when sexually aroused and tugged on just right by a member of the opposite sex, my penis opens a portal to another dimension that I like to call The Phallic Kingdom.